X-ray tube having external means to align electrodes

ABSTRACT

An X-ray tube having at least one electrode connected with the tube envelope so as to provide for alignment of the electrodes. This is implemented by supporting the electrode upon an intermediate member which can be deformed to vary the position of the electrode.

United States Patent 1 Jacob 1 Jan. 30, 1973 'X-RAY TUBE HAVING EXTERNAL [56] References Cited ANS TO ALIGN ELECTRODES ME UNITED STATES PATENTS [75] Inventor: Heinz-Jurgen Jacob, Norderstedt,

Germany 2,058,l05 lO/l936 Pohl ..3l3/60 2,130,020 9/1938 McEven ..3l3/ 6O Assigneel Philips Corporation, New 2,926,270 2/1960 Zunick ..3l3/60 York, N.Y. 3,303,372 2/l967 Geiger"... ..3l3/60 Filed Feb 22 1971 3,398,307 8/l968 Brown etal. ..3l3/60 [21] Appl. No.: 117,436 Primary Examiner-R0y Lake Assistant Examiner-Darwin R. Hostetter Alt0rneyFrank R. Trifari [30] Foreign Application PriorityData March 26, I970 Germany ..P 20 I4 937.5 1 ABSTRAT An X-ray tube having at least one electrode connected [52] US. Cl ..3l3l6lll)bi lg/slgg with the tube envelope so as to provide for alignment 2 4 of the electrodes. This is implemented by supporting le 0 earc the electrode p an intermediate member which can be deformed to vary the position of the electrode.

1 Claim, 2 Drawing Figures 7 III i PATENTEDJAHSOIQB 3.714.487 SHEET 2 OF 2 INVENTOR.

HEINZ-JURGEN JAooB BY M flkwf ENT X-RAY TUBE HAVING EXTERNAL MEANS T ALIGN ELECTRODES The invention relates to an X-ray tube whose electrodes (anode and cathode) are connected with the tube bulb in a vacuum-tight manner.

The bulb of known X-ray tubes usually consists of glass. The anode is then soldered to a ring consisting of an alloy having the same thermal expansion coefficient as glass and sealed-to the bulb by glass. The cathode is usually mounted on a glass pinch. After assembly the ends of the glass bulb and of the pinch are heated, bent over towards each other and-fused together. As a matter of course this method of assembling does not permit an accurate alignment of the anode and the cathode. With X-ray tubes having a long electron path between the filament of the cathode and the target plate of the anode and with X-ray tubes radiating spherically this construction does not always provide useful results. Particularly with the last-mentioned type, in which the anode has the shape of a cone, the upper tapering part of which has to receive the electron beam in order to obtain a uniform radiation intensity in all directions at right angles to the tube axis, the required relative positionsof'cathode and anode have to be accurate within a tolerance of a fraction of a millimeter. Such an accuracy cannot be attained in the known structure.

Moreover in the known X-ray tubes local fusion of the target plate may occur during the first hours of operation and particularly during the running-in period, in which the power of the X-ray tube is gradually raised from an appropriate value to the nominal power. Said fusion is caused by residual gas released from the tube parts upon being heated, said gas being ionized by the voltage applied to the tube and affecting the field so that the electrons, which normally impinge upon a surface of 2 X 3 mms, are focused at one point. At this point temperatures are produced which result in fusion of the electron target plate. The

surface is thus locally roughened so that the useful radiation is reduced. Owing to this substantially potshaped disturbance of the target plate the tube becomes unserviceable, although the further portion of the target plate and the tube are still correct (the residual gas released is bound fairly rapidly by the getters provided).

The invention has for its object to avoid these disadvantages. According to the invention this is achieved by connecting at least one electrode, preferably the cathode, with the tube bulb by way of a deformable intermediate member, the deformation of which results in a variation of the place of the focal spot.

In general it is efficient to connect only the cathode through such an intermediate piece with the bulb of the tube, because the cathode has a smaller weight than the anode. The deformable intermediate piece permits of shifting the cathode and the anode relatively to each other so that, for example, with conical anode X-ray tubes the focal spot is accurately concentrical to the tip of the conical anode. in X-ray tubes whose target plate is sealed at one place the focal spot can be located on an undamaged surface portion.

The drawing shows an embodiment of the invention, wherein FIG. 1 is a cross sectional view and P10. 2 a plan view of an X-ray tube embodying the invention and a device for varying thefocal spot location is shown. 7

For the sake of clarity the connection of the anode 2 with the glass bulb l is not shown in the drawing: it may i be made in known manner by means of a ring of an alloy (tradename Vacon) having the same heat expansion coefficient as glass, one end of said ring being soldered to the anode and the other end being sealed to the glass bulb. in this way a rigid connection is established between the anode and the glass bulb.

The cathode 3 comprises a filament 4 and a cathode pot 5 acting upon the electron path, which elements are secured to a plate 6, to which is furthermore secured an external protecting cylinder 7 of nickel. The plate 6 is held by a metal sleeve 8, which is slipped on a further metal sleeve 9, to which it is secured. The metal sleeve 9, whose end projecting into the glass bulb is hermetically closed by a glass passage, is secured to a disc 11, from which it protrudes over about 10 mms. The disc 11 is secured to a ring '12 of Vacon, which is sealed in turn to the giass bulb 1. The connection between the parts 5 to 9 and 11, 12 of the cathode may be established in known manner by hard solder or by welding.

The positions of the filament 4 and of the cathode pot 5 and hence also the position of the focal spot can be varied in this construction by displacing the sleeves 8 and 9 relatively to the disc 1 1, without an appreciable load on the metal-glass connection between the ring 12 and the glass bulb l. The drawing shows a suitable device for adjusting or displacing the focal spot. It comprises a bipartite sleeve 13, which is slipped onto the ring 12 and is tightened by means of screws 20 (FIG. 2). The lower end of the sleeve 13 has a guide in which a flange l4'can be turned over at least 360 about the axis of the tube. The flange 14 has a tapped hole for receiving a screw 15, the inner end of which is provided with'a suitably shaped extension 16, which engages a tube 17 of hard steel having a thick wall and being slipped into the cathode sleeve 9. The cathode 3, that is to say the filament 4 and the cathode pot, are thus displaced in'the direction of the screw 15, the extent of the deflection being determined by the pressure exerted by the screw 15 on the tube -17.

The adjustment of the focal spot to the tip of the anode cone may be carried out as follows: The X-ray tube driven by nominal voltage and an appropriate cur- 'rent is arranged on a .radiation density container provided with a radiation measuring chamber and turned by means of a motor once over 360 about its own axis. The radiation intensity can be automatically registered in dependence upon the relative angles of rotation. The screw 15 with the flange 14 is moved into the position corresponding to the minimum indication and tightened. The connection between the disc 11 and the sleeve 9 is plastically deformed to an extent such that a repeated measurement exhibits a more uniform distribution of the dosage (deviation smaller than 10 percent) along the periphery.

Owing to the deformation comparatively strong residual stresses are left in the metal parts 9 and 11. Therefore, the screw 15 is loosened so that the cathode slightly returns to its initial position. The final fixation of the cathode can then be performed bymeans of a adjustment is maintained.

in most cases'an adjustment by means of the adjusting device 13 to 17 is even redundant because the adjustment obtainable by means of the assembly 118, 19 is sufficient. However, also in this case, subsequent to the first displacement, the adjusting device has to be released and subsequently retightened, in order to reduce the mechanical stress in the parts 11 and 9.

' Apart from the deformable intermediate piece (8, 9, 11, 12) 7 shown in the drawing, other intermediate pieces may be used. his only essential that the tube should be disposed on a carrier (8, 9), which can be moved from without, while the end of the glass bulb is not exposed to high mechanical stress. For this purpose it is efficient to use between the glass bulb and the sleeve 8, 9 a bottom piece 11 which is at right angles to the axis of the tube and which is bent relatively to the sleeve 8, 9.

What is claimed is: 1. An X-ray tube comprising an evacuated envelope, a plurality of electrodes within said envelope, a deformable rigid intermediate member connecting one of said electrodes to said envelope in a vacuum tight manner for laterally moving one electrode relative to the other, said deformable rigid intermediate member comprising a sleeve supporting the one electrode, a cup-shaped part secured to said envelope and sleeve, said cup-shaped part having a disc-shaped bottom arranged at right angles to said sleeve, and a plate having at least three relatively shifted tapped holes for receiving screws to be tightened against said disc-shaped bottom, and means for deforming said intermediate member to vary the position of the one electrode. 

1. An X-ray tube comprising an evacuated envelope, a plurality of electrodes within said envelope, a deformable rigid intermediate member connecting one of said electrodes to said envelope in a vacuum tight manner for laterally moving one electrode relative to the other, said deformable rigid intermediate member comprising a sleeve supporting the one electrode, a cup-shaped part secured to said envelope and sleeve, said cup-shaped part having a disc-shaped bottom arranged at right angles to said sleeve, and a plate having at least three relatively shifted tapped holes for receiving screws to be tightened against said disc-shaped bottom, and means for deforming said intermediate member to vary the position of the one electrode. 